Method for assembling an electric motor and motor obtained using this method

ABSTRACT

A method for assembling an electric motor of the type comprising a stator unit ( 5 ) and a rotary unit ( 6 ) housed in a containment compartment ( 2   a ) delimited by a casing ( 2 ), comprises the step of exposing the compartment ( 2   a ) to a different pressure relative to the outside environment and the step of checking for the passage of fluid between the outside environment and the compartment ( 2   a ) in order to test the motor ( 1 ) hermetic seal.

TECHNICAL FIELD

The present invention relates to a method for assembling an electricmotor and in particular a watertight electric motor.

Specific reference is made below to an electric motor, although it shallbe understood that the invention may relate to any rotary electricmachine, such as an alternator or a dynamo.

BACKGROUND ART

In general, a rotary electric machine comprises a stator, a rotormounted on a shaft and a casing with supports for the rotor shaft.

To mount the stator and the rotor in the casing, the latter must bedivided into at least two parts which can be assembled.

An example of an electric machine and a method for making it is knownfrom patent U.S. Pat. No. 5,767,596.

Also known, especially in the sector of electric fans for motorvehicles, are watertight and moisture proof electric motors.

Such motors are designed to operate in environmental situations and inpositions in which they may be subject to infiltration by water andmoisture, which may create electrical problems for the motor.

There have been prior art attempts to make a watertight casing forelectric motors, in particular made by inserting a gasket between thetwo parts mentioned above, for example as described in documentWO2005/034309 by the Applicant.

However, this type of assembly is not without disadvantages: inparticular, when the motor is closed, that is to say when the lid andthe cup-shaped part are locked relative to one another, there is noabsolute guarantee that the motor will be hermetically sealed.

Despite the many efforts made to ensure this, the gasket between the twoparts of the casing may not be perfectly positioned or effectivelysquashed to guarantee a suitable seal between the parts in contact.

Moreover, infiltrations may occur at the motor shaft supports, inparticular where the motor shaft comes out of the casing for motoreffectiveness.

DISCLOSURE OF THE INVENTION

In this context, the main technical purpose of the present invention isto propose a method for assembling an electric motor and an electricmotor obtained with this method which are free of the above-mentioneddisadvantages.

One aim of the present invention is to propose a method which allows anelectric motor to be obtained with good hermetic properties.

Another aim of the present invention is to propose a method forassembling an electric motor which is simple and inexpensive toimplement.

The stated technical purpose and aims of the invention are substantiallyachieved by a method for assembling an electric motor as described inclaim 1 and in one or more of the dependent claims herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present invention are moreapparent in the description below, with reference to a preferred,non-limiting embodiment of a method for assembling an electric motor anda motor obtained using this method, as illustrated in the accompanyingdrawings, in which:

FIG. 1 is an exploded side view, with some parts cut away for greaterclarity, of the electric motor in accordance with the present invention,in one step of the assembly method;

FIG. 2 is a schematic top plan view of the motor in accordance with thepresent invention, in an assembly step;

FIG. 3 is a schematic perspective view of a succession of steps ofassembling a part of the electric motor in accordance with the presentinvention;

FIG. 4 is a schematic view of the cross-section IV-IV from FIG. 2;

FIG. 5 is an enlarged view of the detail A from FIG. 4;

FIG. 6 is a schematic side view of an assembly step in accordance withthe present invention;

FIG. 7 is a schematic side view of another assembly step in accordancewith the present invention;

FIG. 8 is a schematic cross-section of a second embodiment of a motor inaccordance with the present invention;

FIG. 9 is a schematic cross-section of a detail of a third embodiment ofa motor in accordance with the present invention;

FIG. 10 is a schematic cross-section and a front view of a detail of afourth embodiment of a motor in accordance with the present invention;

FIG. 11 is a scaled down view compared with the detail from FIG. 10, ofa detail of the fourth embodiment of the motor in accordance with thepresent invention;

FIG. 12 is a schematic cross-section of a portion of the fourthembodiment of the motor in accordance with the present invention;

FIG. 13 is a schematic front view of a lid of a fifth embodiment of amotor in accordance with the present invention;

FIG. 14 is a schematic side view of the lid of FIG. 13;

FIG. 15 is a schematic rear view of the lid of FIG. 13.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

With reference to the accompanying drawings and in particular withreference to FIGS. 4 and 8, the numeral 1 denotes an electric motorassembled in accordance with the present invention.

The description below refers specifically to an electric motor, but itshall be understood that the invention may also relate to other types ofrotary electric machines, for example power generators, alternators andthe like.

The electric motor 1 comprises, schematically, an outer casing 2delimiting a containment compartment 2 a.

The casing 2 consists of a substantially cup-shaped part or container 3and a lid 4 connected to one another with connecting devices of theknown type and therefore not illustrated in detail.

An electromagnetic unit consisting of a stator unit 5 and a rotary unit6, of the substantially known type, is housed in the casing 2.

The rotary unit 6, able to rotate about an axis R, comprises a shaft 7partly projecting outside the casing 2.

As illustrated in FIG. 8, the motor 1 shown is of the so-called“twin-shaft” type, that is to say, the shaft 7 and the casing 2 are madein such a way that the shaft 7 axially comes out of the cup-shaped part3 and the lid 4.

The motor 1 comprises means 8 for supporting the rotary unit 6positioned inside the casing 2.

In particular, the rotary unit 6 is rotatably constrained to thecup-shaped part 3 and to the lid 4 by bearings 9 and 10, respectively.

The bearings 9, 10 are locked to the lid 4 and to the container 3 andthe shaft 7 is inserted in them.

The bearing 9 is of the sealed type to prevent infiltrations fromoutside through the bearing 9.

In the case of a twin-shaft motor 1 the bearing 10 is also preferablysealed.

It should be noticed that the bearing 9 is inserted in a relative cavity9 a made in the base wall 3 a of the cup-shaped part 3, whilst the lid 4has a cavity 10 a for the bearing 10.

The bearing 9 is locked in the cavity 9 a preferably by means ofcaulking, as described in further detail below.

Moreover, in the preferred embodiment illustrated the motor 1 comprisesan O-ring 20 positioned between the bearing 9 and the base wall 3 a.

The motor 1 also preferably comprises a gasket 21, substantiallytubular, positioned between the bearing 10 and the lid 4.

The gasket 21 has an inner lip 21 a positioned between the bearing 10and the lid 4.

In practice, the gasket 21 is inserted in the cavity 10 a and thebearing 10 is in turn inserted in the gasket 21, pressing the inner lip21 a against the lid 4.

FIG. 4 in particular shows how the motor 1 comprises means 11 forsupplying power to the motor 1, said means housed in the casing 2.

In the embodiment illustrated, the power supply means 11 consist of abrush holder 12 of the substantially known type.

It should be noticed that in the exploded diagram in FIG. 1 the brushholder 12 is omitted in order to keep the diagram simple.

In particular with reference to FIGS. 10, 11 and 12, the motor 1comprises a substantially disk-shaped isolating element 28 positioned insuch a way as to protect the lid 4 to prevent accidental short-circuitsbetween the power supply means 11 and the casing 2.

In particular, the isolating element 28 is required if the power supplymeans 11 comprise brushes, not illustrated in detail, supplied by meansof a respective metal braid, also not illustrated, which mayaccidentally make contact with the lid 4.

The isolating element 28 has a central hole 28 a surrounding the cavity10 a of the bearing 10 and an opening 28 b for supplying power to thepower supply means 11 as described in more detail below.

It should be noticed that the gasket 21 preferably has an outer lip 21 bfor holding the isolating element 28 in the correct position relative tothe lid 4, in particular when the lid 4 is assembled on the cup-shapedpart 3.

Advantageously, the gasket 21 has a pair of annular thickened portions21 c for obtaining a seal between the bearing 10 and the relative cavity10 a.

To guarantee the motor 1 an effective seal against external agents, themotor has a gasket 13 positioned between the lid 4 and the cup-shapedpart 3.

With reference to FIGS. 1, 4 and 8, the gasket 13 is preferably of thetype illustrated in the above-mentioned document WO2005/034309 which isincorporated herein by reference as a non-limiting example and forcompleteness of description.

Alternatively, the gasket 13 is directly moulded on the lid 4 tosimplify motor 1 assembly, that is to say, the lid 4 is made during afirst moulding step, and the gasket 13 is provided on the lid 4 during asecond moulding step.

As illustrated in FIG. 9, in a different embodiment, a sealing material30 is positioned between the lid 4 and the cup-shaped part 3 to form aseal between them.

In the embodiment illustrated, the sealing material 30 is positioned onthe lid 4 whilst, in alternative embodiments not illustrated, thematerial 30 is positioned on the edge of the container 3.

The lid 4 preferably has an annular groove 30 a suitably shaped toreceive the sealing material 30.

In a preferred embodiment, the sealing material 30 comprises anadhesive.

Advantageously, in another embodiment, the sealing material 30 comprisesa polyurethane material.

In that case, a polyurethane foam is dosed in the annular groove 30 a.The foam polymerises, substantially resulting in the formation of agasket having a waterproof outer surface which encloses a foamy corewith damping function particularly advantageous for taking up lid 4closing play and tolerances.

FIG. 5 in particular shows how the shaft 7 has a substantially annularcavity 14, for an annular gasket 15 between the shaft 7 and the bearing9.

As illustrated in FIG. 8, the shaft 7 has a second annular cavity 16 fora relative substantially annular gasket 17.

As illustrated in FIG. 3, the lid 4 has an opening 18 for connection ofthe power supply means 11 to an external cable 19.

The motor 1 preferably comprises an interconnecting element 22 insertedin the opening 18 where the power supply means 11 are associated withthe cable 19.

In particular the power supply means 11 comprise a pair of pins 11 a,lib which are positioned in the opening 18 when the lid 4 is positionedon the cup-shaped part 3.

The interconnecting element 22 has a pair of openings 22 a, 22 b throughwhich the pins 11 a, 11 b come out of the lid 4.

The cable 19 is associated with the pins 11 a and 11 b, preferably bysoldering.

A closing element 23 is inserted in the opening 18 to seal the opening18, as described in more detail below.

The element 23 has a hole 24 for injecting a sealing material into theopening 18.

It should be noticed that the opening 18 and the closing element 23 areshaped in such a way as to allow the cable 19 to pass to the outside ofthe casing 2.

The method for assembling the motor 1 comprises the steps of insertingthe stator unit 5 in the cup-shaped part 3 and locking it to the latterin a relatively known way.

The rotary unit 6 supporting means 8, in particular the bearing 9, arelocked in the base wall 3 a of the cup-shaped part 3.

The bearing 9 is inserted in the cavity 9 a together with the O-ring 20and locked in positioned by caulking the cavity 9 a.

The rotary unit 6 is then inserted in the cup-shaped part 3substantially at the stator unit 5.

In particular, the shaft 7 is inserted through the bearing 9 andconstrained to it.

It should be noticed that the gasket 15, preferably of the “O-ring”type, being pressed in the cavity 14 between the shaft 7 and the bearing9, guarantees a motor 1 seal against external agents where the shaft 7comes out of the casing 2.

As illustrated in FIG. 8, in a substantially similar way, in the case ofa twin-shaft motor 1, the gasket 17 pressed in the cavity 16 between theshaft 7 and the bearing 10 guarantees a seal against external agents atsaid bearing 10.

The brush holder 12 is inserted in the cup-shaped part 3 and the lid 4is positioned in such a way that it closes the part 3.

It should be noticed that during this step the lid 4 is not locked tothe cup-shaped part 3, but is placed in the position it has on thefinished motor 1 and held there.

It should be noticed that if the isolating element 28 is required, it isheld in the correct position by the gasket 21 outer lip 21 b.

Preferably, with the motor 1 in this configuration, several electrictests are carried out in the substantially known way.

In particular, the motor rpm, noise and amperage draw are tested.

As illustrated in FIG. 6, with the lid 4 positioned on the cup-shapedpart 3 and the casing 2 substantially closed, the motor 1 hermetic sealis tested.

The motor hermetic seal is preferably tested at the end of the electrictests.

The motor 1 hermetic seal is preferably tested by exposing the casing 2and therefore also the compartment 2 a to a different pressure relativeto the outside environment.

In particular, the motor 1 hermetic seal is tested by detecting anypassage of a fluid between the outside environment and the compartment 2a after application of said difference in pressure.

In the preferred embodiment illustrated the step of exposing thecompartment 2 a to a different pressure is carried out by blowing a gasinto the casing 2 to bring the pressure in the compartment 2 a to valueshigher than the outside environment, that is to say, exposing thecompartment 2 a to an overpressure relative to the outside environment.

In particular, pneumatic means 25, of a substantially known type, areput in fluid communication with the inside of the casing 2.

In more detail, a hood 26 rests on the lid 4 in a hermetic way and thepneumatic means 25 engage the opening 18 in a sealed way.

The pneumatic means 25 blow a gas into the casing 2 and if no gas leaksout of the casing 2 then the motor 1 is definitely sealed.

Preferably, during the action of the pneumatic means 25 theinterconnecting element 22 is inserted in the opening 18.

Advantageously, the motor 1 hermetic seal can be tested by means of asucking action from the inside of the casing 2 towards the outside. Thepneumatic means 25 put in fluid communication with the compartment 2 asubstantially suck air out of the compartment 2 a until a vacuum iscreated in it, that is to say, the compartment 2 a is subjected to alower pressure than the outside environment.

If, as the sucking action is continued, air passes from the outsideenvironment into the casing 2, this shows that the motor is nothermetically sealed.

It should be noticed that the step of testing the motor 1 hermetic sealand the electric tests may be carried out in the same test station.

If the tests are carried out manually by an operator, they arepreferably carried out in the same station, for example the station 27illustrated in FIG. 6.

Advantageously, when the motor 1 is assembled in a production line, notillustrated, the electric and hermetic seal tests are carried out in twoseparate stations.

When the tests are complete, the casing 2 is closed, that is to say, thelid 4 and the cup-shaped part 3 are locked relative to one another inthe substantially known way.

The cable 19 is soldered to the power supply means 11 at the connectingelement 22.

Once the lid 4 has been locked on the cup-shaped part 3 and the cable 19has been connected to the power supply means 11, the opening 18 issealed.

The closing element 23 is inserted in the opening 18 and driven into it.

As schematically illustrated in FIG. 7, the sealing material, preferablyadhesive, is then injected, in a substantially known way, into theopening 18 through the hole 24 in the closing element 23.

It should be noticed that the connecting element 22 functions as anelement for collecting the sealing material and the opening 18 iscompletely sealed.

Another motor 1 hermetic seal test is preferably advantageously feasibleonce the motor has been assembled, in particular if using the brushholder lid 4 a.

In this case, the lid 4 a, with the sealing material 30 on it,preferably adhesive, is used to close the container 3.

The motor 1 is immersed in a test liquid to check if any of the liquidenters the compartment 2 a.

The motor 1 seal is preferably tested after thermal transients.

The motor 1 is heated then immersed in the test liquid.

Preferably, once it has cooled, the motor 1 is heated again thenimmersed in the fluid, which must not penetrate the motor 1 after thethermal expansions due to the sudden changes in temperature.

This procedure may be repeated several times as necessary.

It should be noticed that the hermetic seal test involving immersion inthe test fluid is feasible with any type of motor 1.

In particular with reference to FIGS. 13, 14 and 15, it should benoticed that the hermetic seal test involving immersion in the testfluid may advantageously be carried out on motors 1 comprising themoulded lid 4 also functioning as the brush holder 12 support.Hereinafter, for the sake of simplicity, said lid 4, moulded andcomprising the brush holder 12, will be referred to simply as the brushholder lid 4 a.

Such motors do not have openings giving access to the compartment 2 a,since the brush holder lid 4 a substantially houses a pin 29 forconnecting the lid 4 a to the external cable 19 in a substantially knownway.

It should be noticed that in such motors the seal between the brushholder lid 4 a and the container 3 is preferably obtained using thesealing material 30.

The sealing material 30 used with the brush holder lid 4 a preferablycomprises an adhesive.

In another embodiment, the sealing material 30 comprises a siliconematerial or a polyurethane material.

The sealing material 30 is preferably placed directly on the lid 4 awhen lid moulding is completed.

Advantageously, in an alternative embodiment, not illustrated, the brushholder lid 4 a is closed on the cup-shaped part 3 by inserting arelative gasket, as well as the sealing material, between them.

Advantageously, said gasket is moulded on the brush holder lid 4 a, thatis to say, the brush holder lid 4 a is obtained in a first moulding stepand the gasket is provided on it in a second moulding step.

The invention brings important advantages.

Thanks in particular to the hermetic seal test carried out withpneumatic means, the motor seal, created as a result of the gasketspresent on the shaft, the gasket between the lid and the cup-shaped partand the special bearings used, is effectively tested.

Said step is easy to carry out and so relatively inexpensive.

Further seal guarantees are supported by the tests which may be carriedout on the motor after thermal transients.

The invention described above may be modified and adapted in severalways without thereby departing from the scope of the inventive concept,as defined in the claims herein.

Moreover, all the details of the invention may be substituted bytechnically equivalent elements.

1. A method for assembling an electric motor comprising a casing (2)delimiting a compartment (2 a) containing an electromagnetic unit (5, 6)consisting of a stator unit (5) and a rotary unit (6), the casing (2)comprising a substantially cup-shaped part or container (3) and aclosing lid (4, 4 a), the method being characterised in that itcomprises the step of testing the motor hermetic seal by exposing thecontainment compartment (2 a) to a different pressure relative to theoutside environment.
 2. The method according to claim 1, characterisedin that the step of testing the motor hermetic seal comprises the stepof testing for the passage of a fluid from the outside environment tothe compartment (2 a) or vice versa.
 3. The method according to claim 1,comprising the steps of: inserting the stator unit (5) in the container(3); locking the stator unit (5) relative to the container (3);providing means (8) for supporting the rotary unit (6) in the casing(2); inserting the rotary unit (6) in the container (3) substantially atthe stator unit (5), the rotary unit (6) being constrained in particularto the supporting means (8); associating power supply means (11) withthe electromagnetic unit (5, 6); providing sealing means (13, 30)between the lid (4, 4 a) and the container (3); associating the lid (4,4 a) with the container (3).
 4. The method according to claim 1,characterised in that the step of exposing the containment compartment(2 a) to a different pressure comprises the step of blowing a gas intothe casing (2) to create an overpressure in the compartment (2 a)relative to the outside environment.
 5. The method according to claim 1,characterised in that the step of exposing the containment compartment(2 a) to a different pressure comprises the step of sucking a gas out ofthe casing (2) so that the pressure in the compartment (2 a) is lowerthan in the outside environment.
 6. The method according to claim 1,characterised in that the step of exposing the containment compartment(2 a) to a different pressure comprises the step of putting thecompartment (2 a) in fluid communication with pneumatic means (25)through an opening (18) in the casing (2).
 7. The method according toclaim 1, characterised in that the step of exposing the containmentcompartment (2 a) to a different pressure comprises the step ofimmersing the motor in a test liquid, the step of testing for thepassage of a fluid between the outside environment and the compartment(2 a) comprising in particular the step of testing for the passage ofthe test fluid into the compartment (2 a).
 8. The method according toclaim 1, characterised in that step of testing the motor hermetic sealis carried out substantially when the motor is subjected to temperaturetransients.
 9. The method according to claim 6, characterised in thatthe opening (18) is present for connection of an external cable (19) tothe power supply means (11).
 10. The method according to claim 9,comprising the step of inserting in the opening (18) an interconnectingelement (22) where the power supply means (11) are connected to thecable (19).
 11. The method according to claim 9, comprising the step ofsealing the opening (18) in particular at the end of the motor hermeticseal test step.
 12. The method according to claim 11, characterised inthat the sealing step comprises the step of applying a closing element(23) to the opening (18), the closing element in particular allowing thepassage of the cable (19).
 13. The method according to claim 12,characterised in that the step of applying a closing element (23) to theopening (18) comprises the step of at least partly inserting the closingelement (23) in the opening (18).
 14. The method according to claim 11,characterised in that the sealing step comprises the step of injecting asealing material, preferably adhesive, in the opening (18), inparticular through a hole (24) made in the closing element (23).
 15. Themethod according to claim 3, characterised in that the step of providingmeans (8) for supporting the rotary unit (6) in the casing (2) comprisesthe step of associating with the container (3) a watertight bearing (9)having a relative O-ring (20) in a cavity (9 a) suitably made in a basewall (3 a) of the casing (2).
 16. The method according to claim 11,comprising the steps of: providing a substantially annular cavity (14,16) on the shaft (7); inserting a substantially annular gasket (17, 15)in the cavity (14, 16), the gasket (15, 17) being used to create a sealbetween the shaft (7) and the bearing (9, 10).
 17. The method accordingto claim 1, comprising the step of locking the lid (4, 4 a) to thecontainer (3).
 18. The method according to claim 3, characterised inthat the sealing means (13, 30) comprise a gasket (13) positionedbetween the lid (4, 4 a) and the container (3).
 19. The method accordingto claim 18, characterised in that the gasket (13) is mounded on the lid(4, 4 a), said lid (4, 4 a) preferably being obtained in a firstmoulding step and said gasket (13) in a second moulding step.
 20. Themethod according to claim 3, characterised in that the sealing means(13, 30) comprise a sealing material (30) positioned between the lid (4,4 a) and the container (3).
 21. The method according to claim 20,characterised in that the sealing material (30) is an elastomeric orsilicone material.
 22. The method according to claim 21, comprising thestep of dosing the elastomeric or silicone material (30) on the lid (4,4 a), said lid (4, 4 a) in particular being at least partly made bymoulding in a single body with the power supply means (11) to form abrush holder lid (4 a).
 23. The method according to claim 20,characterised in that the sealing means (13, 30) comprise a polyurethanesealing material (30).
 24. (canceled)
 25. (canceled)
 26. (canceled)